The present invention is broadly directed to the preparation of polyisobutylene sealants.
Polymers such as polyisobutylene have found applications in building sealants due to an inherent air and moisture impermeability. To function as a sealant, a curable group is usually combined with the isobutylene units, resulting in, for example, alkoxy-silane functionalized polyisobutylene. Current polyisobutylene building sealants are often formed using a two-step process. The polymer backbone is formed and endcapped with a reactive functional group. The reactive functional group is then reacted, often in the presence of a metal catalyst, resulting in the presence of a curable group on the polymer backbone. In one specific example, the polymer is endcapped with allyl groups through the use of allyltrimethylsilane. Then, the allyl group is hydrosilylated using a platinum catalyst and an appropriate silane. In another method, the reactive functional groups are dispersed throughout the polymer backbone, followed by the reaction of the functional groups to form curable siloxane groups within the polymer backbone. This two-step process is both expensive and cumbersome.
In U.S. Pat. No. 4,829,130, a method is provided for forming silylated derivatives of polyisobutene. The method includes copolymerizing isobutene with an unsaturated comonomer containing halo-silane functionality. The polymerization is initiated by Lewis acid catalysts, with the preferred catalyst being AlCl3. Once the copolymerization is complete, an aliphatic alcohol containing 1 to 5 carbon atoms is added to convert the chloro-silane groups in the polymer backbone to alkoxy-silane groups. The polymer thus formed is an alkoxy-silane functionalized copolymer including isobutene monomer units and alkoxy-silane functionalized comonomers. The process to synthesize the copolymer requires that the monomers not contain functional groups that may interfere with the polymerization catalyst. That an alkoxy silane functionalized monomer was not directly polymerized with isobutene indicates the recognition in the art that the employed Lewis acid catalyst may react with ethers, ketones, amines, imines, nitrides and thioethers. Accordingly, and as evidenced in U.S. Pat. No. 4,829,130, the direct copolymerization of isobutylene with an alkoxy functionalized comonomer would not be contemplated.
It would be desirable to have available a less expensive, more efficient process to directly prepare alkoxysilane functionalized polyisobutylene with lower polydispersity.